Many types of input devices are available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens, and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens generally allow a user to perform various functions by touching (e.g., physical contact or near-field proximity) the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
A touch sensor panel can be coupled with an actuator to form a depressible button. For example, a trackpad can include a touch sensor panel with a continuous top surface and a portion of the continuous top surface forming a depressible button. In some cases, the touch sensing functionality may only be used to determine the touch context when the button is depressed. However, frequently scanning the touch sensor for touch events when the button is not depressed can be an inefficient use of power, especially in mobile devices running on battery power.